Electric lamp



ELECTRIC LAMP Filed May 8, 1919 I INVENTOR 4/ bar hf (ompfm 7 'ATTORNEY Patented Novf3,

:umrao STATES PATENT OFFICE earner. OOIPTON, orvwmirinssnno, Pmmiaem .sssrcutonro winemanousn nurr conrm, a conrom'rron or rmsnvanra morale w Application and m .a, 1919. Serial no. cause.

This invention relates to electric lamps, and, more particularly, to those of the vapor yp v A feature of-the invention is a method of e operating a vapor or gas-filled lamp at the best efficiency, from the standpoint of efi'ective radiation emitted, This includes means for increasing the amount of effective light produced for a given power consumption.

Another object of the invention is to pro-v vide anorganization of certain elements or 'instrumentalities which may produce a gas or vapor'lamp that is self-starting and free from line ballast/ usually employed in the operation of an arc device.

. vA special object of the invention is to provide means for securing a highly luminous,

electric dischar is through sodium vapor in such a manner t at as large a part as posslble of the light emitted shall lie in the characteristic yellow or D lines.

" crease the general efliciency of a gas or vapor Further objects of the invention relates to novel combinations or circuit arrangementsa-nd/details of construction, tending to in arc device of this particular character, as will hereinafter more fully appear.

As is known, there are three critical potentials which may become manifested in the operation of a metallic vapor lamp. These potentials determine the nature of the colli sion between atoms and-electrons moving with velocities imparted by the operating voltage impressed upon suitable electrodes. The are characteristic of the atom with which the electron. collides,difiering as regards the atoms-of different metallic elements but remainingconstant, under varying conditions, as regards. the atoms of'any'one metallic vap r- I It "has bei'i' shown-that, if an. atom of a metallic vapor is struck by an electron, at

' Another feature of the invention is the reg nance potentlal,

a great many wave-lengths. tron, moving at such velocities, collides with y an atom, the ener bounds elastically from the atom, the only energy lost by the electron being the small amount taken up by the rebound of the atom.

Secondly, if the electron is moving with a velocity equal to, or slightly greater'than, that corresponding to a fall through the .resoit may cause the atom to emit radiation the spectrum of which consists of a single line. atom to produce this resonancespectru the electron rebounds elastically, as in the first instance. In any case, practically all of the ener which type of co lision appears as light of the Wave ee'ngth'corresponding to this single spectrum "Thirdly, if the potential through which the electron falls is further increased, another critical velocity is attained, where, at least for many metallic elements, the atom may .emit light of'another definite wave-length.

When an electron havin a speed sli htl in excess of this-second ci itica g y with an atom loses by the collision appears as light of either the first or seconddefinite wave-length.

Fourthly, if the potential through which the electron fallsis further increased ,to the so-called ionizing potential, which is over twice that required to produce resonance, 9. third critical the atom may be excitedto emit its complete' radiat1on, which consists of light of When an elecwhich it loses, is radiated by the atom in light covering a large range of wave-lengths. Additional types of COlllSlOIlS may occur but these four, at least, are known. v

In order to obtain as large anamount of light as possible from the electric ener put into a vapor, the conditions should so adjusted that the electronic collisions will If it does not cause the the electron loses in'this value collides the energy which .the electron velocity is reached, upon which electrons,

. suflicient resonance,

and the atoms of the vapor. But, pressure -is sufiiciently increased, the

stable without any a cathode occur at such speeds that the particular type of radiation is emitted to which the eye is most sensitive. Thus, in the case of sodium vapor, electronic collisions of the second, or type cause the atom to consisting wholly of the yellowffl) lines, to which the eye is highly sensitive, sionsof the'third type have not as yet been observed, but collisions of the fourth type produce a complete radiation to which the e e is not nearly as sensitive as it, is to the yellow light produced by collisions of the secondtype. For this reason it is advantageous, have as many of the-electronic collisions as possible occur at velocities under that corresponding to the ionizing potential.

- This condition can be secured ideally if the cathode of the sodium vapor lamp is heated to incandescence by. an auxiliary source of energy so as to give off a stream of-thermoand if a potential difference of about 3 volts, which is between the resonance and the ionizing.potentials,.is applied between the anode and the cathode. The radiation emitted in this case by the sodium vapor is practically wholly yellow light but its intensity is too low for practical use. In order to increase the amount of lightemitted, it is necessary to increase the number of collisions which-produce resonance. This may be done by increasing the voltage applied between the anode and the cathode. The volt-v age may be raised to a value which is slightly less than the ionizing potential of the vapor,

without producing 1onization; Another way of increasing the number of collisions and therefore the amountof light is-to increase the vapor pressure, I prefer to increase the light by the latter method. If the pressure 0 the sodium vapor is low and the distance between the anode and cathodesmall, a large number of ionizing collisions will occur be tween the electrons given off by the cathode if'the vapor collisions of the electrons wi h the atoms will be so frequent that a resonance collision, absorbing most of the electrons kinetic energy, will probably occur before-the electron can attain speed to produce ionization. Thus, it is possible .to cause practically allthe radiation from the sodium vapor to be ofthe yellow .resonance type, and, at the same time, to obtain a brilliant light.

At the same time, if the cathode of the I lamp is made of material, such as tungsten,

which does not emit electrons underthe influence of the light emitted by sodium vapor, the electric discharge through the lampis .line ballast. If the were some other material,,such as sodium, which would emit electrons when 7 under the influence of the light emitted from the vapor of sodiumfthe electric discharge emit light Co ll'iin the case of a sodium vapor lamp, to V nected to a suitable source of trons and effects the stance 4;Whenever the electrons moving bethrough the lamp would be unstable without line ballast. Thisphenomenon can possiblybe. explained as follows An increase .in. the voltage between the amount of light and this increased amount of light would, in turn, cause more electrons to be emitted from the cathode, which'is the wellfiknown photo-electric effect. The resulting increased number of electrons emitted would produce morev light and the cycle exist. Furthermore, since practically all the the electrodes would increase,

electronic collisions are of the resonance type,

a'slight increase in voltage across the lamp merely increases the number of resonance collisions and does not produce ionization, so that the current through the tube is not materially changed.

" In the accompanying drawings, Fig. 1 illustrates, diagrammatically, an electric lamp of thegas or vapor type embod ing the features above discussed and opera 1e by means of alternating current; and, Fig. 2 illustrates a modification operable by means current.

Referring to Fig. 1 of the drawings, the vapor-arc device shown comprises an exhausted sealed container 1, having pairs of leading-in conductors 2 sealed into the ends thereof and terminatin' in incandescent electrodes or. filaments 3 {0 such as tungsten. Adrzlriliary-current sources are required for heati g the electrodes 3 and they may beindependent/of each other or be obtained from a common source through the agency of a translating device, such as an auto-transformer, as will be explained later. A vaporizable substance 4 having lowvapor pressure, such as sodium, mercury, or the like, is inserted within the container 1, and, when in a vaporized state, becomes luminous by reason of the passage of a current between the electrodes 3. Theconductors 2 are connected, by leads 5 and 6, to the taps of an auto-transformer 7, which, in turn, is conalternating current. These connectionsmay be made in any approved manner and will vary with the operating elficiency of the starting filaments 3. It-will be noted thateach. of the auxiliary circuits is connected in'the main operating circuit, which permits applying the full line voltage between the electrodes.

Upon closing the operating circuit,feach of the filaments 3 is rendered incandescent.-

The heat therefrom produces thermo-elecvaporization of the sub- '"out, in order that-the ilight shall be produced of direct Y refractory material,

would repeat itself. But with a cathode such 75 as eificiently as possible, it is essential that thevapor pressure he kept so high that comparatively few of the electronic collisions can i v roduce ionization of the-sodium molecules.

, will serve as the principal starting'rheost-at 15, in order to prevent a' destructive are from forming in the lamp be- T fore the, vapor pressure of the sodium has become suflicient to prevent any appreciable, ionization.

In Fig. 2 I have illustrated a direct-current device provided with a starting electrode or cathode 8, comprising an arcing tip 9 connected to 'a support 10, the latter being designed to have sufiicient resistance to the conduction of heat to enable the arcing tip 9 to operate at incandescence. The support 10 is also connected to the conductor 5. The starting filament 11 is coiled about the cathode support 10 and connected thereto near 'the tip 9. The opposite-end of, filament 11 is connected to the conductor 6. The anode 12 may have any convenient shape, having regard for proper heat-dissipating capacity,

T and may consist of any suitable refractory material.

The operation of the form of lamp just described is as follows The filament 11 of the cathode 8 is heated to incandescence by' the application of suitable current. This will all] and efi'ect the formation cause the volatilization of the substance 4 of an are between the cathode and the anode which will persist by reason of a flow of the operating current through the leads 5 and 13.

I have foundthat, if the vaporizable substance used is sodium, no series resistance is required in the-line circuit, as is customarily employedin this type of device, and, further,

' that the lamp will be self starting. It is also possible to employ various'e protectingrthe glass, of which t e container is made,

by using a i the container with some suitable tra ombeing attacked by the sodium gas which will surround the column of sodium vapor and prevent the latter from conglass. Like results may betacting with the obtained by coating the interior surface of arent coating which will be unafiected by. e so,-

iumvapor While I have described and illustrated certain embodiments of my invention, these are illustrative rather than definitive, as it is, of 'course;possible to vary the structural details and arrangements of the parts without dients for protective mantle of some suitable departing from the spirit or scope of the invention as defined in the appended claims.

What is claimed is:

1. The method of converting electrical energy into light which consists in passing an electrical discharge between an incandescent cathode and an anode through sodium vapor and maintaining the pressure of said vapor at a value at which a luminous discharge is produced having a stable electrical characteristic.

2. An electrical device comprising the combination of a sealed envelope, a refractory cathode adapted to operate at incandescence, an anode and a quantity of alkali metal within said envelope, said device having a heat dissipating capacity adapted to maintain. the

vapor pressure of said alkali metal at a value at which an electrical discharge therethrough has stable electrical characteristics.

3. An electrical discharge device comprising the combination of a tungsten cathode, an anode, means for heating said cathode, an enclosing'bulb and a quantity of sodium in said bulb. said lamp being roportioned to maintain the vapor pressure oi said sodium below the value at which the volt-ampere characteristic of a" discharge therethrough becomes negative. 4. An electrical device comprising the combination of an enclosed envelope, a cathode adapted to operate at 'incandescence, an anode, and -a quantity of sodium in said envelope. said envelope being proportioned to operate at a temperature at which the va or pressure of said sodium is 'sufliciently high to enable an'electricdischarge therethrough' to ionize said vapor but below the valueat which a discharge through said device has a negative volt-am re characteristic.

5. The method 0 increasing the currentcarrying capacity of an electron discharge which consists .in maintaining in the path of said discharge the vapor of an alkali metal within pressure limits sufiiciently high to L;

cause substantial positive ionizatioh by col 6. An electrical discharge device compris- 3 ing an evacuated envelope, electrodes therein, meansfor'heating one of said electrodes to incandescence independently of a discharge therebetweem, an alkali metal contained therein, said device being constructed to maintain the vapor pressure of alkali metal during operation high enough to increase the current carrying capacity of" said device, but below the value at which an arc-like disharge of negative volt-ampere character- ,istic' may occur. I v v 7 An electrical discharge device comprising a sealed evacuated envelope, a filamentary cathode consisting of refractory material, terminal conductors therefor whereby a heating current may be conveyed to said cathode. an anode, and a quantity of alkah' vmetal in. said envelo e, said device being proportioned, when issipating heat under ordinary external conditions, to operate at a temperature at which the vapor pressure of said alkali metal is sufliciently high to enable an electric discharge therethrough to ionize said vapor but below the value at which a dischargethrough said device has a negative volt-ampere characteristic.

8. An electrical discharge dev ce comprising an hermetically sealed envelope, elec-- trodes within said envelope comprising a solid cathode adapted to be heated to give electrons and an anode, an ionizablemedium within said envelope, the temperature to which said cathode is heated and the heat dissipating characteristics of said envelope beingdesigned to maintain the medium within the envelope at a pressure whereby a stable electrical discharge between the electrodes occurs upon heating the cathode to electron emitting temperature and applying a poten: tial between the electrodes sufficient to ionize the gaseous medium.

9. An electrical discharge device comprising an hermetically sealed envelope, electrodes within said envelope comprising a solid thermionic electron-emitting cathode and an anode, an ionizable medium within said envelope, the temperature to which said cathode is heated and the heat-dissipating characteristics of said envelope being .designed to maintain the medium within the envelope at a pressure whereby upon heating the cathode to electron-emitting temperature and applying a potential between the electrodes substantial; ionization occurs but not suflicient to cause the discharge between the electrodes to have a negative volt ampere characteristic.

In testimony whereof, I have hereunto subscribed my name this 6th day of May, 1919.

ARTHUR H. COMPTON. 

